The most common domestic wastewater treatment system used today in rural areas is the septic tank-soil absorption system. An underground septic tank removes settleable and floatable solids from the wastewater by forming, respectively, a sludge component and an upper scum component. The soil absorption field then filters and treats clarified tank effluent and distributes it throughout the soil. Removing solids from the wastewater in this manner protects the soil absorption system from clogging and failure.
Abstracts are provided for the following recent patents or applications dealing with the subject of septic or related systems and improvements thereon, namely, U.S. Pat. Nos. 4,527,319 (Rosenbaum et al.), 4,605,501 (Tyson), 5,194,144 (Blough), 5,380,427 (Foss), JP 7233532 (Toda Kensetu KK), JP 88022880 (Maruichi Seisakusho), CN 1041805 (Lu), and SU 1654478 (Sirotinski et al.),
Conventional septic systems typically remove solids by holding wastewater in an underground tank. The heavier solids are allowed to settle to the bottom as sludge, and the lighter particles float to the top in order to form a scum layer. As the system is used, the sludge layer continues to accumulate in the bottom of the tank. Properly designed tanks provide enough space for two to three years of safe accumulation of sludge. If too much sludge accumulates settling occurs more slowly, or not at all, meaning that more solids may escape into the absorption area. To prevent this, the tank must be pumped periodically.
Underground tanks are typically cleaned by pumping the contents to a tanker truck using equipment specially designed for the job. See, e.g., R. Machmeier, "Town and Country Sewage Treatment", University of Minnesota Extension Service.
The removal of septic tank contents, and particularly the solids, is a difficult and time-consuming process. The job typically needs to be performed by a professional technician having adequate equipment, including a tanker truck. The first task involved in cleaning a tank is to break up the upper scum layer, and cause it to be reconstituted with the liquid layer and sludge. Over time, the scum layer can become hardened and quite difficult to break. Yet it must be broken, and resuspended with the other layers in order to be removed.
Typically cleaning is accomplished by a backflushing process, using the pump on the tanker trunk. A portion of the liquid layer is first drawn up and then rapidly expelled back into the tank under pressure to agitate all the solids into suspension. This process is repeated several times before the contents can be removed. If the scum layer is hard, it may also be necessary to agitate the tank with air or to use a long-handled shovel through the manhole to break up the sum. When all the solids have finally been resuspended, the mixture (known as septage) is pumped out of the septic tank into the pumper tank.
This backflushing process can often take over an hour or more, particularly with systems that have not been cleaned for an extended period, and/or in situations in which the tank truck is far from the tank (thereby decreasing the available pressure).
What is clearly need are means for improving the ability to break the upper crust or scum layer within a tank, in order to simplify and speed the process of cleaning septic tanks.